I recently started getting some under extrusion issues in my prints, I have had issues with prints not holding water before, however I have never had an issue this big before.
The nozzle has been cleaned recently, using the 'atomic' method, but also by heating the heaterblock and nozzle assembly and blowing compressed air through backwards.
STL files are treads by LoialOtter on thingiverse:
printed using the default 'fast'settings in Cura for the Ultimaker original.
I hope I have provided enough information, if not I'd be happy to provide more as needed.